The present invention refers to a heat exchanger plate for a plate heat exchanger, wherein the plate includes an edge, which extends around the plate, an edge area, which extends around the plate inside the edge, and a heat exchanging surface with a corrugation of ridges and valleys, which extend in at least a first direction over the plate. The invention also refers to a plate package for a plate heat exchanger, and to a plate heat exchanger.
Such heat exchanger plates for rotation of a quarter of a round are known from EP-A-165 179. The plates have a substantially square shape and form a plate package where the inlets and the outlets extend through the sides of the plate package, i.e. the heat exchanger media flow into and out of the plate package in a direction which is substantially parallel to the main extension plane of the plates. Each plate has four side edges, wherein two opposite side edges are folded downwardly and the two other opposite side edges are folded upwardly. Every second plate is rotated 90° in the plate package, wherein the downwardly folded side edges of a plate abut the upwardly folded side edges of an adjacent plate, wherein these side edges are connected to each other by means of a weld joint. In each corner of each plate a tab is formed, which extends along a diagonal direction and in a plane that is substantially perpendicular to the extension plane of the plates.
The plates disclosed in EP-A-165 179, have an active heat exchanging surface with a corrugation of ridges and valleys, which extend in a diagonal direction that is inclined 45° to the side edges of the plates. In the plate package the ridges and valleys of adjacent plates will cross and support each other in a plurality of support points. In an inner area of the heat exchanging surface each support point will carry a load corresponding to the pressure multiplied by the square spacing, but in an outer area of the heat exchanging surface in the proximity of the side edges the load in each support point becomes significantly larger. Due to reasons of the manufacturing technology, a corrugation may not extend to the side edges but there has to be an edge area in order to enable, for instance, bending of the edge. The edge area may in principle be only a substantially line-shaped bending area but preferably the edge area has a substantially plane surface that has a width of 10–15 mm. The design means that the loaded surface becomes significantly larger for the outer support points than for the inner support points. In the two corners, which have support points most far out in the corners, the support points are especially heavily loaded since these are to carry the load from two plane edge areas meeting in the corners.
The pressure performance of a plate is determined by the most loaded support point, which in this case are the two support points in the corners. The load to be carried by these support points is twice the load carried by the inner support points. For a large plate these two support points may be less than 0,1% of the number of support points, which means that more than 99,9% of the plate is over-dimensioned with 100%.